Many Phone Numbers Are Not Listed in Telephone Books

Multiple Choice

Many phone numbers are not listed in telephone books.How do surveyors combat this issue?

A) Surveyors call cell phones.
B) Surveyors call listed numbers and triangulate with another method such as face to face interviews.
C) Surveyors are going away from land line survey methods because of this issue.
D) Surveyors use random digit dialing to formulate their call lists.
E) all of these are ways surveyors combat this issue.